Rotary mowers operate by having a generally planar blade that rotates around its midpoint (a blade rotation axis perpendicular to the blade plane) in a plane substantially parallel to the ground over which the mower runs. The blade typically has two cutting edges, one on each of opposed sides of the blade's longitudinal axis. One cutting edge extends from one distal end of the blade toward the midpoint of the blade along one edge of the blade, and the other cutting edge extends from the opposite distal end of the blade toward the midpoint of the blade along the opposite edge of the blade from the first cutting edge. The cutting edges must be sharpened periodically to provide desired mowing capabilities, including a clean cut, which may affect grass look and health. Given their high rotational speeds, the blades must also be properly balanced.
Known devices for sharpening the edges of such mowing blades may employ one or more grinding wheels provided in a fixed position against which the edges of the blade to be sharpened are moved in order to grind the cutting edges to the desired sharpness. Such sharpening devices may use a flat grinding wheel that performs the grinding operation using the outer circumference of the grinding wheel, i.e., a surface parallel to the wheel's axis of rotation. An example of such a known sharpening device is described in U.S. Pat. No. 6,471,569.
Such sharpening devices have a number of drawbacks. For example, such devices may require that the grinding wheel(s) be adjusted on two planes in order to achieve the correct grind angle. This angle can change, for example, due to rotary blade width changes or grinding wheel wear, and therefore may require additional adjustments for each blade to be sharpened to maintain the correct grind angle. Those adjustments slow sharpener throughput when large numbers of blades need sharpening.
Also, once the grinding has been performed, the blade must be removed from the device and checked for balance, which can be affected by the grinding process. If the blade is not in balance, the blade must be reinserted into the sharpening device and re-sharpened so as to remedy imbalance, then again removed and rechecked for balance. This process is repeated until the blade is balanced. Again, this slows sharpener throughput.
In view of these and other drawbacks of the known sharpening devices, there is a need for an improved device and method for sharpening rotary mower blades.